The present invention relates to a sprocket wheel for advancing a film in a movie camera, a movie projector, a film printer or a telecine and to a device for advancing a film using said sprocket wheels.
A conventional device for advancing a film one frame at a time in a movie camera, a movie projector, a film printer or a telecine is shown in FIG. 1.
In FIG. 1, reference character a denotes a horizontal shaft supported by bearings (not shown) so as to be driven by a motor (not shown); b, a triangular cam attached to the horizontal shaft a; c, a cam follower in the form of a yoke which diametrically clamps the cam b and which is horizontally reciprocable in a direction of double-pointed arrow D.sub.1 depending upon rotation of the cam b; d, an arm mounted on the cam follower c in parallel with the direction of reciprocation of the follower c; e, registration pins attached to a free end of the arm d so as to be disengaged from perforations g on a film f at opposite sides thereof (See FIG. 2) by reciprocal movement of the cam follower c upon the advancement of the film f.
Reference character h designates a further horizontal shaft rotatably supported by bearings (not shown) and having a portion i rectangular in section; and j, a further arm with a rectangular opening k through which the arm j is slidably fitted over the portion i. The arm j has one end to which claws 1 are attached so as to engage with the perforations g shown in FIG. 2 by rotation of the cam b upon the intermittent or frame-by-frame advancement of the film f. The other end of the arm j is pivoted on the cam b at a point 0.sub.2 eccentric to an axis 0.sub.1 of rotation of the cam b.
Further, reference character m denotes a guide of the film f. Though not shown, there are take-off and take-up reels upwardly and downwardly of the film f shown in FIG. 1 so as to wind off the film f and wind up the unwound film f traveling in a direction of arrow D.sub.2, respectively.
In the conventional film advancement device shown in FIG. 1, the motor (not shown) is driven to rotate the horizontal shaft a which in turn rotates the triangular cam b. Rotation of the cam b causes the cam follower c to be moved toward and away from the film f, which causes the registration pins e at the free end of the arm d to be engaged with and disengaged from the perforations g. The arm j is also moved toward and away from the film f to engage and disengage the claws 1 with and from the perforations g.
In frame-by-frame advancement of the film f, the cam b is rotated in a counterclockwise direction to respectively disengage the pins e from and engage the claws 1 with the perforations g and to slide the arm j relative to the portion i and swing the same about an axis 0.sub.3 of the shaft h. As a result, the claws 1 are displaced downwardly to advance the film f only one frame at a time in the direction D.sub.2.
When the advancement of the film f by one frame is finished, the arm j is retracted to disengage the claws 1 from the perforations g to thereby stop the film f; and the cam follower c is advanced to engage the pins e with the perforations g to thereby hold the film f in position so as to be immovable vertically and horizontally. While the the film f is being stopped in position, the cam b is further rotated to return the arms d and j to their initial positions and to respectively disengage the pins e with and engage the claws 1 with the perforations g. This step is repeated to intermittently advance the film one frame at a time.
Another example of conventional film advancement devices is disclosed in U.S. Pat. No. 4,697,896 in which a motor is driven to rotate sprocket wheels for advancing a film. In the system, intermittent advancement of the film by one frame is carried out such that feed or advanced length of the film is determined on the basis of number of rotations per unit time of a motor which is detected by a tachometer as well as number of interruptions per unit time of light beam by a slot disk mounted coaxially with the sprocket wheels or number of transits per unit time of light beam through a slot on the slot disk. That is, advancement of the film by a predetermined length is arithmetically grasped to de-energize the motor and stop the film.
The prior art shown in FIG. 1 has the following problems or disadvantages:
(i) The mechanism for advancing the film is much complicated in structure and in movement so that fast-forward or the like advancement of the film at high speed cannot be carried out by the mechanism itself;
(ii) when it is therefore desired to advance the film at high speed, the film f must be removed or disengaged from the film advancement system shown in FIG. 1 and threaded through a specially designed mechanism so that the whole installation becomes larger-scale; and
(iii) in the case the system shown in FIG. 1 being used for a movie camera or a telecine where a film to be advanced has been developed and therefore has perforations with deteriorated accuracy, excessive force tends to act on the film f by means of the claws 1 in frame-by-frame advancement of the film, resulting in any damages such as fracture of the film f at a corner of the perforation g.
In the film advancement device disclosed in U.S. Pat. No. 4,697,896, advancement and stoppage of the film are electrically carried out so that there arises a problem of frame-by-frame advancement of the film and holding of the same in position being carried out with a low degree of accuracy as compared with the devices using the registration pins.
In view of the above, a primary object of the present invention is to improve accuracies in frame-by-frame advancement of a film and in holding of the same in position so that even in a high speed film advancement, no additional device or installation is required and damages to the film is eliminated.